fix(mcp-v2): don't claim relay-tunnel disconnects mean toggle is off

[saddlepaddle]

Summary

• The relay returns 503 {"error":"Host not connected"} whenever tunnelManager.hasTunnel(hostId) is false (apps/relay/src/index.ts:55-56). That fires for several distinct conditions: toggle off, desktop app closed, WebSocket dropped mid-session, tunnel auth failed during WS upgrade, or tunnel not yet established.
• describeRelayFailure in packages/mcp-v2/src/host-service-client.ts named only the toggle case and pushed a remediation step that's wrong in the other scenarios.
• Replaces the message with a terse statement of fact (Host <id> relay tunnel is not connected.) matching the surrounding 'You are not authenticated' / Host ${hostId} not found style.

Skipped the optional relay-side enrichment ({ error: 'host_not_connected', reason: ... }) — it's a non-trivial cross-package change, would need new types, and wasn't required for the fix. Leaving for a follow-up if we want to surface the actual disconnect reason.

Test plan

• bun run lint:fix clean
• bun run typecheck clean
• Verified no other consumers in the repo key on the old string (the toggle UI label in apps/desktop SecuritySettings is a separate independent string)

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Summary by cubic

Fix inaccurate error text for relay 503 "Host not connected" responses. Now shows "Host relay tunnel is not connected." instead of telling users to enable remote access, which was wrong for cases like app closed, dropped WS, auth failure, or a not-yet-established tunnel.

^{Written for commit b6a7b6f. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Improved error messaging for host connection failures to provide clearer feedback when a host becomes unavailable.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a2ea07ba-f8df-4883-974c-3f60334aa3ae

📥 Commits

Reviewing files that changed from the base of the PR and between 611ab0c and b6a7b6f.

📒 Files selected for processing (1)

• packages/mcp-v2/src/host-service-client.ts

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📝 Walkthrough

Walkthrough

A single error message in the host relay failure handler was updated to provide clearer indication of tunnel connectivity status. The 503 error response message for disconnected hosts now reports the specific host ID and relay tunnel state instead of settings guidance.

Changes

Relay Error Message Update

Layer / File(s)	Summary
Error Message packages/mcp-v2/src/host-service-client.ts	503 "host not connected" error message in describeRelayFailure changed to report Host ${hostId} relay tunnel is not connected. instead of settings guidance.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

A rabbit hops with glee so bright, 🐰
Error messages now shine with light!
No more confusion, just the truth—
When tunnels fail, we speak the proof.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and specifically describes the main change: fixing an inaccurate error message that incorrectly claimed relay-tunnel disconnects mean the toggle is off.
Description check	✅ Passed	The description provides comprehensive context, explains the problem, describes the solution, justifies design decisions, and includes test verification. All critical sections are well-documented.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/mcp-tunnel-error-message

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[greptile-apps]

Greptile Summary

• Narrows the scope of describeRelayFailure in host-service-client.ts: the 503 "Host not connected" branch previously claimed the desktop toggle was off and prescribed a specific remediation, but that 503 fires for several other conditions (WebSocket drop, tunnel auth failure, app closed, not-yet-established tunnel). The new message is a neutral statement of fact.
• The change is a one-line error-message correction with no behavioral side effects; it only affects the human-readable string surfaced in HostServiceCallError.message.
• No new code paths, no type changes, no consumer breakage (the PR description confirms no callers key on the old string).

Confidence Score: 5/5

Safe to merge — one-line error message correction with no logic, API, or type changes.

The change is a pure string replacement in a single branch of a private helper function. It cannot introduce regressions, break types, or affect control flow. The PR description confirms no callers rely on the old string.

No files require special attention.

Important Files Changed

Filename	Overview
packages/mcp-v2/src/host-service-client.ts	Single-line fix replacing a misleading, toggle-specific error message with a neutral "relay tunnel is not connected" fact statement; no logic changes.

Sequence Diagram

sequenceDiagram
    participant Client as MCP Client
    participant Relay as Relay Server
    participant Host as Desktop Host

    Client->>Relay: POST /hosts/{routingKey}/trpc/{procedure}
    alt tunnel connected
        Relay->>Host: forward request
        Host-->>Relay: tRPC response
        Relay-->>Client: 200 OK
    else tunnel not connected (toggle off / WS dropped / auth fail / app closed)
        Relay-->>Client: 503 {"error":"Host not connected"}
        Note over Client: describeRelayFailure()<br/>OLD: "Host X has not enabled remote access. Toggle..."<br/>NEW: "Host X relay tunnel is not connected."
    end

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[github-actions]

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